stack chart tooltips.diff

diff --git a/src/components/stack-chart/Canvas.js b/src/components/stack-chart/Canvas.js
index c7d71e30..a5a1fe0b 100644
--- a/src/components/stack-chart/Canvas.js
+++ b/src/components/stack-chart/Canvas.js
@@ -420,8 +420,14 @@ class StackChartCanvas extends React.PureComponent<Props> {
 
     const stackTiming = stackTimingByDepth[depth];
 
-    if (!stackTiming.callNode) {
-      return null;
+    if (stackTiming.markerIndex) {
+      const markerIndex = stackTiming.markerIndex[stackTimingIndex];
+      return (
+        <TooltipMarker
+          marker={getMarker(markerIndex)}
+          // and the other OwnProps
+        />
+      );
     }
 
     const callNodeIndex = stackTiming.callNode[stackTimingIndex];
@@ -454,10 +460,12 @@ class StackChartCanvas extends React.PureComponent<Props> {
     });
   };
 
+  // This will need to handle marker indexes, maybe returning a new type
   _getCallNodeIndexFromHoveredItem(
     hoveredItem: HoveredStackTiming | null
-  ): IndexIntoCallNodeTable | null {
+  ): {| index: number, type: 'marker' | 'call-node' |} | null {
     if (hoveredItem === null) {
+      // TODO - This will also need to be taught about marker index.
       return null;
     }
 
diff --git a/src/components/tooltip/CallNode.js b/src/components/tooltip/CallNode.js
index 14b180e7..5005d0e4 100644
--- a/src/components/tooltip/CallNode.js
+++ b/src/components/tooltip/CallNode.js
@@ -41,6 +41,7 @@ type Props = {|
   timings?: TimingsForPath,
 |};
 
+// This is the one that is already being used.
 /**
  * This class collects the tooltip rendering for anything that cares about call nodes.
  * This includes the Flame Graph and Stack Chart.
diff --git a/src/components/tooltip/Marker.js b/src/components/tooltip/Marker.js
index b8b644f8..24817a1e 100644
--- a/src/components/tooltip/Marker.js
+++ b/src/components/tooltip/Marker.js
@@ -643,6 +643,7 @@ function getMarkerDetails(
   );
 }
 
+// These are the OwnProps which will need to be passed in from the stack chart.
 type OwnProps = {|
   +marker: Marker,
   +threadIndex: ThreadIndex,
@@ -719,6 +720,7 @@ class MarkerTooltipContents extends React.PureComponent<Props> {
   }
 }
 
+// Here is the tooltip component for markers, which needs to be added.
 export const TooltipMarker = explicitConnect<OwnProps, StateProps, {||}>({
   mapStateToProps: (state, props) => {
     const { threadIndex } = props;